Design Blog: HMS Unicorn – An Evolutionary Ship

Design Blog: HMS Unicorn – An Evolutionary Ship

As we celebrate one month since the opening of V&A Dundee, we thought it timely to explore Unicorn’s fascinating design and incredible 194 year history.

Interestingly, V&A Dundee is actually built on the location of Unicorn’s original home in Earl Grey Dock when she arrived in the city in 1873. There she stayed until 1962 before moving to her current home at Victoria Dock. An important part of Dundee history, she easily predates most of the buildings in the city centre, and had already been in Dundee for 50 years when the Caird Hall was opened.

In 2014 Dundee was named ‘UNESCO City of Design’ thanks to the city’s diverse contributions to fields including medical research, comics and video games. Receiving this prestigious title combined with Dundee’s ongoing waterfront redevelopment has drawn tremendous attention to the importance and prominence of ingenious design in the city.

 

Here, Professor Emeritus David Bradley looks at how design was instrumental in instructing Unicorn’s unique construction.

On first thoughts, many would imagine that the most noteworthy thing about Unicorn is her longevity having spent almost 200 years afloat, with over 100 of those years (1873 to present) being spent in Dundee. Closer inspection reveals that she is in fact an example of a key moment in the design of naval vessels, one that resulted in the transformation over the 100 years from 1805 to 1906 from navies based on sailing warships – the Wooden Walls – to ones based on armoured and steam powered vessels – the Dreadnoughts.

To understand how huge this change was, imagine you were a seaman on Henry VIII’s Mary Rose in 1545. Then go forward 260 years to HMS Victory at the Battle of Trafalgar in 1805. Although there would be some differences, Victory essentially sailed, fought and functioned in exactly the same manner as the Mary Rose.

 

HMS Dreadnought

Now go forward a further hundred years, to 1906 and HMS Dreadnought and you would be in an entirely alien environment. Gone are the sails and the wooden construction to be replaced by steam turbines and steel armour. Gone are the rows of muzzle loading cannon with ranges of 2 to 3,000 metres to be replaced by turrets carrying breech loading guns capable of firing 12-inch explosive shells weighing 850 pounds (~ 386 kg) distances in excess of 12 miles (~ 19 km).

In this context, Unicorn represents a significant transitional stage in warship design in which the use of new materials such as wrought iron enabled design changes which led to significant improvements in respect of hull performance, sailing qualities and seakeeping.

Throughout the 18th and the early part of the 19th century, the design of ship’s hulls had evolved relatively slowly, based on a process of making small incremental changes and then evaluating each change. If a change proved beneficial, it was carried forward to other ships; if not it was rejected.

By 1822 when Unicorn was laid down, though the basic underwater hull form remained viable, developments in manufacturing technology were making new materials, such as wrought iron of consistent quality, more readily available. At the same time, an increasing shortage of wood meant that naval architects were increasingly looking to utilise such materials. Further, ships of the period were reaching a size limit imposed by the physical properties of wood when used as a structural material.

 

Among those leading these innovative developments was Robert Seppings who became joint Surveyor of the Navy in 1813. As Surveyor, Seppings assumed overall responsibility for the design and construction of Royal Navy vessels at the Royal Dockyards and oversaw the introduction of several major design developments into ships built under his charge, all of which can been seen in Unicorn, herself laid down at Chatham in 1822, and launched in 1824.

Seppings introduced a rounded stern, adding strength to what had conventionally been a weak point of the hull, wrought iron knees to support the deck beams and transfer load to the frames and diagonal and other bracing in the form of wrought iron straps throughout the lower hull.

HMS Unicorn’s Iron Knees

 

These changes improved seakeeping – the way a ship goes through the waves – made her drier and reduced maintenance requirements. All of which improved the ability to remain at sea for long periods.

They also increased the resistance of the hull to gunfire, at least with regard to the roundshot used by contemporary cannon, while providing a more robust and stable gun platform in return.

Despite the design innovations incorporated into her construction, Unicorn also represents the end of the sailing ship navy. In 1827, three years after Unicorn was launched, came the Battle of Navarino Bay, the last battle fought entirely by sailing warships. The day after the battle the steam warship Karteria, designed and built in Britain at Rotherhide on the Thames and in service with the Greek navy, entered the bay.

 

Blog by Professor Emeritus David Bradley, HMS Unicorn Volunteer